Excessive water production or a thief zone during the production phase of a subterranean formation penetrated by a well can decrease hydrocarbon production or increase costs of well operations. The amount of oil and/or gas that may be ultimately recovered from the well is decreased since the water takes the place of other fluids that may flow or be lifted from the well. Thus, excessive water production has a direct affect on the productivity of the well and increases operating expenditures. In addition, expenditures are increased due to the need for disposal of produced water in an environmentally safe manner.
In the past, gel systems have been used to control water production and reduce the flow of produced water through high permeability channels within the formation. Such gellants plug pore spaces of the formation and prevent fluid movement, often by means of a controlled, delayed chemical reaction, such as precipitation or swelling.
For instance, success has been reported with three-dimensional crosslinked polymer gel systems. Such systems include a base polymer and a crosslinking agent, both of which may be liquid concentrates in water. Depending on formation temperatures, varying ratios and concentrations of the base polymer and crosslinking agent are mixed in water and then pumped into the formation. The reaction between the base polymer and the crosslinking agent creates a strong gel barrier which shuts off or reduces water production.
For use in low temperature reservoirs, it is highly desirable for the gel systems to react quickly. A system presently used in such reservoirs is based on polyacrylamide and a metallic crosslinker, such as chromium. Representative chromium crosslinkers include chromium acetate and chromium chloride. Such crosslinkers promote a rapid exchange between the metal and the ligand of the polymer. Gelation typically occurs in less than 12 hours with low thermal activation. Treatment of reservoirs having a temperature lower than about 150° F. is possible. However, chromium based crosslinkers are not allowed in some areas due to environmental regulations.
As demands have been made for environmentally friendlier treatment chemicals, alternative systems have been sought.